This book covers the main ideas, methods, and recent developments of quantum-limit optical spectroscopy and applications to quantum information, resolution spectroscopy, measurements beyond quantum limits, measurement of decoherence, and entanglement. Quantum-limit spectroscopy lies at the frontier of current experimental and theoretical techniques, and is one of the areas of atomic spectroscopy where the quantization of the field is essential to predict and interpret the existing experimental results. Currently, there is an increasing interest in quantum and precision spectroscopy both theoretically and experimentally, due to significant progress in trapping and cooling of single atoms and ions. This progress allows one to explore in the most intimate detail the ways in which light interacts with atoms and to measure spectral properties and quantum effects with high precision. Moreover, it allows one to perform subtle tests of quantum mechanics on the single atom and single photon scale which were hardly even imaginable as ``thought experiments'' a few years ago.

Zbigniew Ficek is a professor at the King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia. He graduated from the Adam Mickiewicz University, Poznań, Poland and worked for many years at the University of Queensland, Australia, where he was ARC QEII Fellow, Senior Research Fellow and then Professorial Research Fellow. He also worked at the Queens University of Belfast as UK EPSRC Professorial Research Fellow. His research speciality is quantum optics and quantum information. He is particularly well known for his contributions to the ﬁeld multi-atom effects, spectroscopy with squeezed light, quantum interference and multi-chromatic spectroscopy. He is the co-editor of a book on Quantum Squeezing, the author and co-author of over 160 scientiﬁc papers, a research book on Quantum Interference, and two textbooks on Quantum Physics for Beginners and Quantum Optics for Beginners.

Ryszard Tanaś is a professor in the Faculty of Physics at Adam Mickiewicz University, Poznań, Poland. Since 1993 he has served as Head of Nonlinear Optics Division. His research focuses on theoretical quantum optics and quantum information. He is the recipient of the Wojciech Rubinowicz Award of the Polish Physical Society.